The clinical practice will show whether a preoperative calculation of expected prosthesis length in MS based on the length of the formerly used stapes prosthesis is possible and helpful.
In contrast to the ideal reconstructive situation, the present data show a malleus-stapes offset with particular unfavorable angles for a stapes head to malleus tip assembly.
Prostheses replacing the incus in its normal position and equipped with two joints might transfer sound as effectively as the intact ossicular chain and allow adjustment to quasi-static pressure changes. A prerequisite for prostheses development is the access to dimensions and distances of the ossicular chain which are necessary to conceptualize shape and size. Fifteen cadaveric human temporal bone specimens were investigated by means of micro-CT followed by 3D analysis. Each specimen was scanned three times: after removal of incus, after additional removal of the malleus head, and after approaching the umbo to the promontory. Artificial umbo medialization as a surrogate for quasi-static pressure changes leads to relevant variations in the distance between the upper part of the malleus and the stapes. Prostheses replacing the incus in its normal position should be equipped with a sliding ball joint or similar construction to allow adjustment to quasi-static pressure changes.
Over the course of the last decade 3D printing has become a more established technology in terms of prototype development (rapid prototyping). The current effort is focused on transferring this knowhow into a product driven approach in order to manufacture even small batch sizes more economic. In terms of this work, this idea is adapted for the development of injection molds (rapid manufacturing). Hereby, a hardened polymer is used to create a forming cavity instead of tool-steel. In order to fulfil the mechanical process requirements of micro injection molding such as form stability under temperature and pressure this cavity is nevertheless integrated into a metal housing. A first set of experiments has been carried out using this develop mold to verify the capabilities of the developed prototype as well as molding process. Based on these first results, an optimization is carried out to improve the next iteration of this molding tool.
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